The present invention relates to a method for controlling a flow rate of a liquid, in particular of a molten material, between a maximum flow and a zero flow, in a valve comprising at least a fixed plate and a mobile plate which are superposed and maintained constantly in contact with each other, each one presenting at least an opening, said method consisting of placing said openings more or less opposite to each other by displacing said mobile plate.
The actually known valves or stop-valves, particularly those applied in the metallurgy and especially in continuous casting, are divided into two types, namely a first valve type, the mobile plate of which is moved in two senses according to a rectilinear direction for forming a slide system and a second valve type the mobile plate of which is provided for being moved according to a circular motion for putting in both senses its opening or openings opposite or aside of an opening present in the fixed plate.
First these known valves or stop-valves, whatever their type may be, have the disadvantage of causing, when moving the mobile plate and especially when moving it for reducing or interrupting the liquid jet, a wear which is located on a relatively reduced part of the border of the opening of the mobile plate which, on the one hand obliges to increase the amplitude of the movement of the mobile plate for a given flow rate when the degree of the wear increases and, on the other hand, which has for consequence an increasing deviation of the jet resulting in an increase of the turbulences and an enhancement of deposits of chemical compounds and/or of solidified metal under the fixed plate and in the collector gas-nozzle cooperating with the opening of the latter, with the result that the disturbances of the jet are further increased and this until the interruption of the latter.
Although, it has been already considered to displace the mobile plate in both senses of the rectilinear (slide) or circular directions (rotary type) to cope with said disadvantage, it is however not possible with respect to the path followed by the mobile plate, to spread the wear over the whole periphery of the opening or the openings of said mobile plate.
Consequently, the two known valve types require to replace the mobile plates, which are expensive components, even as to interrupt the operation of the device for replacing the valve involving considerable costs whereas said mobile plates are only partly worn or degraded.
Moreover, said valves have other serious drawbacks, more particularly: considerable degradation risks due to tensions which are not homogeneous owing to the irregular heating of different masses, irregularly distributed around the opening of the mobile plate and eventually of the fixed plate; degradation risks due, for the same reason, to the different heat losses within the plates and finally, degradation risks due to local heatings in extremely reduced zones of the mobile plate, and always in the same zones.